Monitoring moderate Cu and Cd toxicity by chlorophyll fluorescence and P700 absorbance in pea leaves

We investigated the effect of moderate Cu²⁺ and Cd²⁺ stress by applying chlorophyll (Chl) fluorescence and P₇₀₀ absorbance measurements to monitor the photosynthetic electron transport activity of 3-week-old Pisum sativum L. cv. Petit Proven?al plants grown in a modified Hoagland solution containing 50 ??M CuSO₄ or 5 ??M CdCl₂. Both heavy metals caused a slight inhibition in PSII photochemistry as indicated by the decrease in the effective quantum efficiency of PSII (??_PSII), the maximum electron transport capacity (ETR_max), and the maximum quantum yield for electron transport (??). PSI photochemistry was also affected by these heavy metals. Cu²⁺ and Cd²⁺ decreased the quantum efficiency of PSI (??_PSI) as well as the number of electrons in the intersystem chain, and the Cu²⁺ treatment significantly reduced the number of electrons from stromal donors available for PSI. These results indicate that PSII and PSI photochemistry of pea plants are both sensitive to moderate Cu²⁺ and Cd²⁺ stress, which in turn is easily detected and monitored by Chl fluorescence and P₇₀₀ absorbance measurements. Therefore, monitoring the photochemistry of pea plants with these noninvasive, yet sensitive techniques offers a promising strategy to study heavy metal toxicity in the environment.